The present invention relates generally to a method of manufacturing valves and is more particularly directed to a process of making cooled valves for internal combustion engines as well as by way of new industrial products the valves obtained by carrying out said method.
As known, the so-called mushroom-type or tulip-shaped or poppet valves cooled by a cooling medium or coolant are made in at least two parts, namely: the head or disc and the stem or spindle, with a view to providing the coolant feed and return flow ducts or channels, respectively, therein. Both parts are then assembled or connected together either by being screwed into each other or by being welded or brazed together or by being hooped, clamped or similarly bound to each other.
Such assembling processes suffer however from certain drawbacks. In the case of welded constructions, breaking failures are likely to occur in view of the sensitiveness or tendency to cracking of the materials generally used for making valves.
In the case of brazed structures, the assemblies are likely to undergo damages, loosenings, separations, partings or like impairments owing to differential heat expansion phenomena. In the case of screwthreaded constructions, gradual unscrewings or like loosenings have been noticed under the combined action of differential thermal expansions and vibrations to which the valves were subjected.
The inconveniences mentioned hereinbefore would most frequently result in the detachment through breaking failure of the valve head or disc and its dropping or falling into the engine working cylinder thereby causing very substantial damages.